1. Field of the Invention
The present invention relates to an image projection apparatus configured to project an image in such a manner that trapezoidal distortion of the projected image is corrected, and a control method and a program thereof.
2. Description of the Related Art
When an image is projected on a screen by an image projection apparatus such as a projector, trapezoidal distortion of the image occurs depending on the projection angle. A keystone correction is performed to an input image to correct the distortion so that the input image and the projection image become geometrically similar. If the keystone correction is performed by reducing the input image, band limitation is performed by a low-pass filter before the reduction processing to suppress a moire pattern. The moire pattern is recognized when aliasing distortion occurs.
However, when the band limitation is performed, frequency domain that does not require limitation is also limited. As a result, a problem of a blurred projection image occurs. In response, Japanese Patent Application Laid-Open No. 2005-210418 discusses performing edge enhancement processing to the image obtained after the keystone correction to reduce the blurring of the image.
However, when the edge enhancement processing is performed, if the processing includes processes that enhance a frequency which is higher than a predetermined level, for example, edge extraction using a high-pass filter, the frequency band which has been limited to avoid aliasing is also enhanced. As a result, a moire is formed and further, the moire is enhanced to be projected.